(1) Field of the Invention
This invention concerns a catalytic reforming process including a catalyst collector that is purged with a purge gas stream derived from a net off gas slip stream.
(2) Description of the Art
Current catalytic reforming processes that include catalyst regeneration systems that employ a catalyst collector typically direct a purge gas derived from the recycle compressor discharge into the catalyst collector. Moreover, many catalytic reforming processes use recycle gas compressors having rotors that are continuously or intermittently washed with hydrocarbons. As a result of the hydrocarbon washing of the recycle gas compressor rotors, heavy hydrocarbon components enter the recycle gas stream. The additional heavy hydrocarbons in the recycle gas increases the dew point of the recycle gas to a point where components of the hydrocarbon wash medium can condense in poorly insulated lines or un-insulated flanges, in all ambient temperature conditions.
Where a recycle gas slip stream including heavy hydrocarbon components is directed as a purge gas to the catalyst collector, the deposition of liquid hydrocarbons from the hydrocarbon wash medium and subsequent absorption of hydrocarbons onto the catalyst in the catalyst collector creates a number of additional problems. One problem is that the spent catalyst in the catalyst collector becomes abnormally heavy, resulting in the inability to lift the catalyst from the bottom of the catalyst collector to the top of the catalyst regeneration vessel at normal lift conditions. Another problem that can be caused by the condensed hydrocarbon washing medium is that catalyst particles may adhere to one another preventing catalyst movement and lifting. In addition, normal purge gas exchanger outlet temperatures are not always sufficient to purge absorbed hydrocarbons from the catalyst and, as a result, hydrocarbons can be carried into the lift/dust collection circuit creating unsafe dust removal and hydrocarbon carryover into the catalyst regeneration tower.